The present invention relates generally to an improved lead assembly for use in combination with an implantable pulse generator to form a cardiac pacer apparatus, and more specifically to a system for sealing the lead assemblies into place in the implantable pulse generator so as to accommodate ease of assembly during implant and to resist during the extended implant period, any influx of body fluids which could interfere with normal operation of the pulse generator, and thereby detract from the efficiency of the pacer apparatus.
Cardiac pacers are employed at the present time to treat various problems in the heart, including treatment of arrhythmias or other disorders which require external stimulation to sustain adequate cardiac output. Cardiac pacers in use today include asynchronous units as well as demand-inhibit units, with the selection being indicated by the patient's condition.
Artificial electronic pacers very nearly approximate the electrical impulses normally delivered by the natural cardiac conduction network. These electronic pacers consist of a pulse generator and an insulated conductive wire lead, the pacer emitting small, sequentially timed electrical impulses which cause the ventricular heart muscles to contract. In a normal person, ventricular contractions result from depolarization caused by transmission of signals from the sino-atrial node through the atrial-ventricular node and the Common Bundle (His) to the right and left bundle branches and the Purkinje Network. When a segment of this natural conduction system becomes blocked, such as when there is no conduction through the Bundle of His, an artificial pacer is normally required to maintain an adequate and appropriate heart rate and rhythm.
In an implantable cardiac pacer assembly or system, the combination of a pulse generator and lead is employed, the term "pulse generator" normally refers to the implantable electronic device, while the term "lead" refers to the insulated conductive wire which is electrically and mechanically coupled to the pulse generator and which receives the stimulating impulse from the pulse generator and transmits this impulse to the heart. The lead incorporates an electrode which is the conductive element or contact, normally exposed, on or adjacent the distal end of the lead to establish electrical contact with the heart muscle.
In an implantable system, either endocardial leads or myocardial leads may be employed. Endocardial leads are those leads which enter the heart through a vein and make contact with the endocardium, while myocardial leads are those which are attached to the surface of the heart with an electrode making contact with the myocardium.
Established procedures are employed for the lead placement, with these procedures being well known in the art. Following placement of the lead, electrode thresholds are determined and upon an indication of satisfactory thresholds, the proximal ends of the leads are connected to the pulse generator. This connection is normally accomplished by the insertion of the exposed terminal pin of the lead into the connector block of the pulse generator. Inasmuch as the terminal pin and the connector block have exposed conductive surfaces, it is essential that the zone surrounding the terminal pin-connector block assembly be sealed and maintained free of body fluids. Leakage of body fluids into the cavity or zone occupied by the terminal pin-connector block combination may adversely affect pacer performance, hence durable seals must be provided.
The procedure for inserting the leads into the pulse generator must be one which can be accomplished with a maximum degree of freedom, so as to avoid inadvertent moving of the placed electrode and lead. This requires, in turn, that the insertion of the terminal pin into the connector block be accomplished with ease. Regrettably, as one attempts to facilitate ease of insertion of the terminal pin into the connector block, one further complicates or interferes with normal sealing between the proximal end of the lead and the pulse generator. In accordance with the present invention, however, an improved sealing arrangement is provided which enables ease of insertion of the terminal pin into the connector block, without adversely affecting the quality of the seal.
In order to improve the quality of the seal and for mechanical integrity, the terminal pin extends axially into that portion of the lead which is received within the body of the pulse generator. The terminal pin, which is durable and rigid, preferrably terminates at a point axially spaced inwardly from the zone of the seal. Therefore, the rigid pin may be accommodated within a bore formed in the connector block, with the bore formed in the connector block being of a radial dimension sufficiently great so as to readily receive and accommodate the exposed portion or segment of the terminal pin. Thereafter, when the set screw is forced against the surface of the exposed portion of the terminal pin, any radial deflection of the terminal pin may be accommodated without adversely affecting or destroying the seal established between the lead and the lead accommodating bore formed in the pulse generator.